Playback over WASAPI must match the sample rate of the output device. Thus applications must supply their own resampling if the playback rate does not match. Most applications don't do this but just employ MME or DirectSound, which provide transparent resampling for non-matching rates.

Since some of my content is 44.1 kHz and some 48 kHz I used to set the output rate to 192 kHz so that all audio had to be upsampled. With good software resampling and a cheap onboard codec this could, in theory, even improve the overall result. But the opposite was true. Today I couldn't longer ignore the impression that the resampled output sounded somewhat muffled and did some measurements.

You can view the result here. The upsampled output (44.1 -> 192 kHz) suffers from quite a HF roll-off in comparison to pure 44.1 kHz output.

In Windows XP the SRC quality could be adjusted. I can't find anything comparable in Windows 7. Does anyone know more?

A) WASAPI doesn't force any player to resample. One has to resample only if it uses exclusive mode, and if it uses exclusive mode it's for a reason, not for the operating system to do the work for you.

B) The frequency that is set in the device configuration is precisely the samplerate at which it operates the final mix (if not in exclusive mode), and as such, the sampling rate at which other sources get resampled.

C) I have no idea what you've supposedly done, but let me be doubtful that simply upsampling causes the effect you show (which isn't as big as you try to suggest. It's 7dB! )

D) Please, consider using adequate words in this forum. "This sucks" or "This 0wns" are not adequate words.